Dear all, Apologies if this has been covered already in a previous post — but I can't find a suitable response in the archive. We have the following situation... We have soaked a ligand into an apo-crystal, collected diffraction data, and solved the structure. What is apparent from the electron density, is that the ligand isn't in the crystal at full occupancy, it's roughly about 70-80%. However, as the ligand binds, it causes a small conformation change in the active site of the protein, altering the position of around 4 amino acids. What I want to do, and can't quite get phenix.refine to do is the following... Refine the occupancy of the ligand (chain C resname LIG) with the "A" conformation of the active site residues (which should be the same, as they are mutually dependent) — and then refine the occupancy of the "B" conformation of the active site residues — which should all theoretically add up to a total of 1. Could anyone help me with how the occupancies / constrained_group parameters should be set up in this case? With thanks, Tony. --- Dr Antony W Oliver Senior Research Fellow CR-UK DNA Repair Enzymes Group Genome Damage and Stability Centre Science Park Road University of Sussex Falmer, Brighton, BN1 9RQ email: [email protected]mailto:[email protected] tel (office): +44 (0)1273 678349 tel (lab): +44 (0)1273 677512